Android ViewPager 小圆点指示器

痛定思痛。 2022-08-20 13:07 205阅读 0赞

一个很常用的功能，一个ViewPager会自动滚动，并且有一排小圆点黑和白来指示当前的滚动进度

首先写一个ViewPager的适配器，这里这个适配器为了方便里面的元素全都是ImageView

import android.content.Context;
    import android.os.Handler;
    import android.support.v4.view.PagerAdapter;
    import android.support.v4.view.ViewPager;
    import android.view.View;
    import android.view.ViewGroup;
    import android.view.animation.Interpolator;
    import android.widget.ImageView;
    import android.widget.LinearLayout;
    import android.widget.Scroller;
    
    
    
    /**
     * Created by Administrator on 2016/2/24.
     */
    public class HomeHomeBannerAdapter extends PagerAdapter{
        private Context context;
        private ImageView[] eventImageViews;
        private String[] eventUrls;
        int destWidth,destHeight;
    
    
        public HomeHomeBannerAdapter(Context context, String[] eventUrls,int destWidth,int destHeight) {
            this.context = context;
            this.eventUrls = eventUrls;
            this.destHeight = destHeight;
            this.destWidth = destWidth;
            initImageViews();
        }
    
        /**
         * 初始化viewPager里的几张图
         */
        private void initImageViews(){
            if(eventUrls==null)return;
            eventImageViews = new ImageView[eventUrls.length];
            for (int i=0;i<eventUrls.length;i++) {
                eventImageViews[i] = new ImageView(context);
                eventImageViews[i].setLayoutParams(new LinearLayout.LayoutParams(destWidth, destHeight));
                eventImageViews[i].setPadding(0, 0, 0, 0);
                eventImageViews[i].setScaleType(ImageView.ScaleType.FIT_XY);
                JImageUtils.loadImageFromServerByUrl(context,eventImageViews[i],eventUrls[i]);
            }//显示图片
        }
    
        @Override
        public void destroyItem(ViewGroup container, int position, Object object) {
            if (eventImageViews != null && eventImageViews.length > position && position >= 0)
                container.removeView(eventImageViews[position]);
    
        }
    
        @Override
        public Object instantiateItem(ViewGroup container, int position) {
            container.addView(eventImageViews[position], 0);
            return eventImageViews[position];
        }
    
        @Override
        public int getCount() {return eventUrls==null?0:eventUrls.length;}
    
        @Override
        public boolean isViewFromObject(View arg0, Object arg1) {
            return arg0 == arg1;
        }
    //ViewPager监听器集成到内部类去
        static public class EventViewPagerChangeListener implements ViewPager.OnPageChangeListener {
            LinearLayout llGuideGroup;
            int oldEventPosition;
            int currentItem;
    
            public EventViewPagerChangeListener(LinearLayout llGuideGroup){
                this.llGuideGroup = llGuideGroup;
            }
    
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {}
    
            /**
             * 控制小点的白色还是黑色的显示
             * @param position
             */
            public void onPageSelected(int position) {
                llGuideGroup.getChildAt(oldEventPosition).setBackgroundResource(R.drawable.dot_normal);//黑色点
                llGuideGroup.getChildAt(position).setBackgroundResource(R.drawable.dot_focused);//白色点
                oldEventPosition = position;
                currentItem = position;
            }
    
            @Override
            public void onPageScrollStateChanged(int state) {
    
            }
        }
    
        /**
         * 控制viewpager自动滑动的定时任务
         */
        public static class ScrollTask implements Runnable {
            EventViewPagerChangeListener listener;
            ViewPager vpEvent;
            int eventSize;
            Handler handler;
            public ScrollTask(EventViewPagerChangeListener listener,final ViewPager vpEvent, int eventSize){
                this.listener = listener;
                this.vpEvent = vpEvent;
                this.eventSize = eventSize;
                handler = new Handler();
            }
            public void run() {
                if(listener==null||vpEvent==null||eventSize==0)return;
                listener.currentItem = (listener.currentItem + 1) % eventSize;
                Log.i("Alex","currentItem是"+listener.currentItem);
                handler.post(new Runnable() {
                    @Override
                    public void run() {
                        vpEvent.setCurrentItem(listener.currentItem); // 通过Handler切换图片
                    }
                });
            }
        }
    
        public static class FixedSpeedScroller extends Scroller {
            private static final int mDuration = 400;
            private int eventCount;
    
            public FixedSpeedScroller(Context context, Interpolator interpolator,int eventCount) {
                super(context, interpolator);
                this.eventCount = eventCount;
            }
    
            @Override
            public void startScroll(int startX, int startY, int dx, int dy, int duration) {
                if (duration % 100 == 0 && duration > 0) {
                    //"现在是自动划"
                    if (duration / 100 == eventCount) super.startScroll(startX, startY, dx, dy, 1);//如果是最后一张
                    else super.startScroll(startX, startY, dx, dy, mDuration);
    
                } else {
                    // "现在是手动划"
                    super.startScroll(startX, startY, dx, dy, 80);
                }
            }
        }
    }

在上面适配器的内部类有一个监听器，这个监听器里有一个成员LinearLayout llGuideGroup，这个线性布局里面装有几个小点，下面是这个布局的定义

设置小圆点的数量并初始化监听器

/**
         * 向一个线性布局里添加小圆点，具体的控制逻辑在listener里
         * @param llGuideGroup
         * @param count 要添加多少个小圆点
         */
        public EventViewPagerChangeListener addViewPagerDots(LinearLayout llGuideGroup,ViewPager vpEvents,int count){
            if(llGuideGroup==null||vpEvents==null||count<1)return null;
            LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(15, 15);
            lp.leftMargin = 5;
            lp.rightMargin = 5;
            for(int i=0;i<count;i++){
                ImageView imageView = new ImageView(llGuideGroup.getContext());
                imageView.setLayoutParams(lp);
                imageView.setBackgroundResource(i==0?R.drawable.dot_focused:R.drawable.dot_normal);
                llGuideGroup.addView(imageView);
            }
            //控制小圆点显示的监听器
            EventViewPagerChangeListener listener = new EventViewPagerChangeListener(llGuideGroup);
            vpEvents.addOnPageChangeListener(listener);
            return listener;
        }

通过多线程实现定时切换页面

HomeHomeBannerAdapter.EventViewPagerChangeListener listener = producer.addViewPagerDots(holder.llGuideGroup,holder.viewPager,eventUrls.length);//添加用于指示的小圆点
                        // 当Activity显示出来后，每3秒钟切换一次图片显示
                        ScheduledExecutorService scheduledExecutorService = Executors.newSingleThreadScheduledExecutor();
                        scheduledExecutorService.scheduleAtFixedRate(new HomeHomeBannerAdapter.ScrollTask(listener,holder.viewPager,eventUrls.length), 3, 3, TimeUnit.SECONDS);

设置自定义滚动器降低viewPager的切换速度

/**
         * 给ViewPager设置自定义的滚动器，降低默认的滚动速度
         * @param vpEvent
         */
        public void setViewPagerScroller(ViewPager vpEvent){
            if(vpEvent==null)return;
            Field mField;
            Scroller mScroller;
            try {
                mField = ViewPager.class.getDeclaredField("mScroller");
                mField.setAccessible(true);
                mScroller = new HomeHomeBannerAdapter.FixedSpeedScroller(vpEvent.getContext(), new AccelerateInterpolator(),vpEvent.getChildCount());
                try {
                    mField.set(vpEvent, mScroller);
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }
            } catch (NoSuchFieldException e) {
                e.printStackTrace();
            }
        }